Let's do some math ..  Rounding examples of 7 random hypothetical purchases:
Case	Tag   Price	Sales   Tax %	Raw Total   Incl. Sales Tax	Rounded   to Penny	Rounded   to Nickel	Rounded   to Dime
Purchase #1	$32.90	13.291%	$37.2727	$37.27	$37.25	$37.30
Purchase #2	$214.56	11.517%	$239.2709	$239.27	$239.25	$239.30
Purchase #3	$121.27	10.283%	$133.7402	$133.74	$133.75	$133.70
Purchase #4	$178.65	11.748%	$199.6378	$199.64	$199.65	$199.60
Purchase #5	$79.72	3.757%	$82.7151	$82.72	$82.70	$82.70
Purchase #6	$118.54	12.802%	$133.7155	$133.72	$133.70	$133.70
Purchase #7	$37.27	13.335%	$42.24	$42.24	$42.25	$42.20
7 purchase totals =	$782.91		$868.5922	$868.60	$868.55	$868.50